WASHINGTON - President Obama wants Americans to see how climate change will remake their own backyards - and to make it as easy as opening a web-based app.

As part of its effort to make the public see global warming as a tangible, immediate and urgent problem, the White House on Wednesday will inaugurate a website aimed at turning scientific data about projected droughts and wildfires and the rise in sea levels into eye-catching digital presentations that can be mapped using an app.

Mr. Obama's counselor, John D. Podesta, who has been charged with creating a strategy to build political support for Mr. Obama's climate change agenda, and the White House science adviser, John P. Holdren, came up with the idea. In theory, the app, at climate.data.gov, would be a powerful tool, allowing local governments or home and business owners to type in an address - as they do on sites like Google Earth - to quickly see how the projected rise in sea levels might increase the chance that their house will be flooded in the coming years. But in practice, until climate science and mapping applications can live up to the site's ambitions, it will remain very much in its testing phase.

At the beginning, the website will serve chiefly as a clearinghouse for climate science data from the National Oceanic and Atmospheric Administration, the United States Geological Survey, the Defense Department and NASA, according to Mr. Holdren and Mr. Podesta. The first batch of data will focus on coastal flooding and the rise in sea levels.

Average users will not be able to do much yet on their own. Instead, NASA and the NOAA will call on researchers and private companies to create software simulations illustrating the impact of sea level rise.

White House officials say they hope to help recreate the success of desktop and mobile apps and software that were built by private companies using government data, like on the real estate sites Trulia, Redfin and Zillow. Those apps use information from the Bureau of Labor Statistics and the Census Bureau to help families make more informed decisions about buying a house.

Robert M. Pestronk, executive director of the National Association of County and City Health Officials, said he hoped the new climate data tools would help municipal officials plan for climate change. "Local health officials are on the front lines of preparing for and addressing the health effects of climate change - from reduced air quality to extreme weather to climate-sensitive infectious disease like West Nile virus and Lyme disease," he said.

The website, Mr. Pestronk said, "will provide valuable data to guide and support local health departments in their efforts to ensure the health and safety of people in their communities."

But the research and projections on climate change are vastly more nuanced than simple housing, labor and census statistics. While a number of scientific reports have reached the consensus that carbon pollution from the burning of fossil fuels has warmed the planet - leading to a future of rising sea levels, melting land ice, an increase in the most damaging types of hurricanes, and drought in some places and deluges in others - scientists warn against trying to use that data to model precisely what will happen when.

"The essence of dealing with climate change is not so much about identifying specific impacts at a specific time in the future. It's about managing risk," Prof. Chris Field, the director of the department of global ecology at Stanford University, said in February.

"The thing that's important about framing climate change as a risk is that it puts the emphasis where it should be. Not that a specific thing will happen at a certain time - some things are known, some things aren't," said Professor Field, an expert on earth sciences and a member of the United Nations Intergovernmental Panel on Climate Change, a group of scientists that regularly publishes reports on the state of climate science.

Professor Field pointed out that higher emission levels could lead to more intense warming in the coming decades, and thus higher sea levels, but lower pollution levels could lead to different results.

Mr. Obama hopes to make climate change a signature issue of his second term, and the Environmental Protection Agency is working on a pair of highly debated regulations that could cut emissions but would also shutter hundreds of coal-fired power plants, the chief cause of carbon pollution.

Republicans, who have already started to push back, have called the proposed rules a war on coal.

Since joining the White House in January, Mr. Podesta has taken on the uphill task of building a political case for the E.P.A. rules, both by defusing the opposition and building support for them by creating, among voters, an urgent sense that they are necessary. The website is the latest step in that strategy. This year, the White House unveiled a series of regional climate hubs, research centers aimed at highlighting the impacts of climate change on farmers and offering resources to help.

U.N. climate panel: Governments, businesses need to take action now against growing risks

Mark Lennihan/AP - This aerial photo from Oct. 31, 2012, shows the New York skyline and harbor. The vast destruction wreaked by Hurricane Sandy's storm surge in New York could have been prevented with a sea barrier.

By Steven Mufson, Monday, March 31, 3:00

The world's leading environmental scientists told policymakers and business leaders Sunday that they must invest more to cope with climate change's immediate effects and hedge against its most dire potential, even as they work to slow the emissions fueling global warming.

The U.N. Intergovernmental Panel on Climate Change said that climate change is already hurting the poor, wreaking havoc on the infrastructure of coastal cities, lowering crop yields, endangering various plant and animal species, and forcing many marine organisms to flee hundreds of miles to cooler waters.

But the Nobel Peace Prize-winning group said that climate change's effects will grow more severe and that spending and planning are needed to guard against future costs, much as people insure themselves against possible accidents or health problems.

The report said that damage from climate change and the costs of adapting to it could cause the loss of several percentage points of gross domestic product in low-lying developing countries and island states. It added that climate change could "indirectly increase risks of violent conflicts in the form of civil war and inter-group violence" by "amplifying" poverty and economic shocks.

The summary of the report, ratified at a five-day meeting in Yokohama, Japan, avoided specific forecasts or timetables or cost estimates, but it described a range of likelihoods and outcomes in an attempt to give decision-makers the tools to set priorities to combat those effects.

Scientists who helped write the report said that efforts to adapt could include constructing emergency cyclone and flood shelters like those in parts of Bangladesh, moving generators out of New York City basements that flooded during Hurricane Sandy, changing farming techniques to cope with higher temperatures, and conserving water and curbing pollution in areas threatened with more-frequent droughts.

"The focus is as much on identifying effective responses as on understanding challenges," Chris Field, co-chairman of the IPCC working group writing the report, said in a statement last week. On Monday in Yokohama, he said that "we need to think about reducing risks and building more resilient societies" by drawing on "deep pools" of creativity and innovation.

Michael Oppenheimer, a professor of geosciences and international affairs at Princeton University and one of the report's authors, said: "There is a more optimistic tone about our ability to adapt to some of these things. We've had some bad heat waves and coastal storms, and we have a better idea of what we need to do. Whether we will ever do it, I don't know."

But he cautioned that "everyone agrees that if we don't slow the warming down, our prospects for adaptation are not good."

The risk-based approach opened the door to discussion in the report of grave climate scenarios, even if their likelihood is relatively remote, just as a company might plan for an extremely rare flood, earthquake or tornado.

An early draft of the report had estimated that governments would need to spend scores of billions of dollars a year on adaptation efforts, according to a person who saw the early version, but the final summary made no mention of how much money might be needed.

"The IPCC's new report underscores the need for immediate action in order to avoid the most severe impacts of climate change," said John P. Holdren, President Obama's science adviser. "It reflects scientists' increased confidence that the kinds of harm already being experienced as a result of climate change are likely to worsen as the world continues to warm."

The IPCC report said, "Responding to climate-related risks involves decision-making in a changing world, with continuing uncertainty about the severity and timing of climate-change impacts, and with limits to the effectiveness of adaptation."

The impact and adaptation report is Part 2 of a four-part assessment by the IPCC. It relied on about 12,000 papers and was written by 309 scientists, who voted on the final version Sunday morning in Japan.

"For the first time, we have measured in terms of risk so each of the climate risks could be weighed against each other and compared with the risk of this versus the risk of something else," Oppenheimer said.

Jonathan Overpeck, a professor of geosciences at the University of Arizona who also worked on the report, said, "We did that because we deal with day-to-day life by managing risks, and a big part of managing our large corporations is assessing risks and managing those risks."

The "very high confidence" category of climate-change effects included exacerbating more-intense heat waves and fires, increased food- and water-borne diseases, and a steady rise in sea level in certain regions, such as the East Coast of the United States.

The report reiterated warnings that world leaders and businesses must act to slow climate change, not just adapt to it. "Increasing magnitudes of warming increase the likelihood of severe, pervasive, and irreversible impacts," the report said. It said that some of the warming could have "cascading effects."

The report attached a "medium confidence" rating to some of those events, but it highlighted the danger of "abrupt and irreversible regional-scale change" if high temperatures hurt the ability of the Arctic boreal tundra or the Amazon forest to store carbon dioxide, or sped the collapse of a continental ice sheet.

But the most likely damage from climate change will be linked to rising sea levels and temperatures. Those changes could turn the advantages of growing coastal cities into vulnerabilities if interlocking transportation, electrical and information systems fail, Oppenheimer said.

Gary Yohe, an economics and environmental studies professor at Wesleyan University and a co-author of the report, said: "I teach my students that the answer to every economic question is ‘It depends.' You don't want to be poor, you don't want to be young, you don't want to be old, and you don't want to live along the coast."

New York City's Empire State Building, just before going dark for Earth Hour on Saturday. In a Monday report, the United Nations Intergovernmental Panel on Climate Change said global warming is having an impact on human and natural systems on a global scale. Agence France-Presse/Getty Images

TOKYO - Global warming is having an impact on human and natural systems world-wide, scientists warned in a report Monday, calling for swift action to mitigate the impact of greenhouse gas emissions on the planet.

The report, released by the United Nations Intergovernmental Panel on Climate Change, is the second portion of a four-part report, and follows the September release of the first portion, which focused on scientific evidence for global warming.

"What happens in terms of impact of climate change in different parts of the world will be determined to a large extent (by how much) we are prepared and able to mitigate the emissions of greenhouse gasses," IPCC Chairman Rajendra K. Pachauri said.

The report said that besides an increase in global average temperature, climate change was having a widespread impact on everything from water resources to food production and weather patterns.

It said that without action to address the problem, by the year 2100, hundreds of millions of people could be affected by coastal flooding and displaced due to land loss.

"Impacts from recent extreme climatic events, such as heat waves, droughts, floods, and wildfires, show significant vulnerability and exposure of some ecosystems and many human systems to climate variability," the report warned.

The report said climate change may affect the reliability of pipelines and electricity grids, as well as tourism resorts, especially ski and beach resorts.

It also said climate change had the largest impact on people who are socially and economically marginalized.

"Climate change will exacerbate poverty in low and lower-middle income countries, including high mountain states, countries at risk from sea-level rise, and countries with indigenous peoples, and create new poverty pockets in upper-middle to high-income countries in which inequality is increasing," it said.

But funding needed to offset the impact of climate change is lacking, the report warned, saying developing countries would need between $70 billion to $100 billion a year to implement needed measures. And efforts to reduce the effects of climate change would only have a marginal effect on reducing poverty unless "structural inequalities are addressed and needs for equity among poor and non-poor people are met."

The report was the culmination of efforts by hundreds of scientists, and portrays a sobering picture of what civilization may face in the coming decades, and emphasized that climate change is happening now.

"Present-day choices thus affect the risks of climate change throughout the 21st century," it said.

Economically, the report said a global temperature rise of 2.5 degrees celcius above preindustrial levels could lead to global economic losses between 0.2% and 2.0% of income. By the end of the century, it said climate change could reduce labor productivity by 11%-27% in humid, tropical areas.

The IPCC's credibility has come under scrutiny since a 2007 report that contained errors about the pace of the melting of Himalayan glaciers.